On Load Distribution Factors In Continuous Slab Girder Bridges

Author : Hani Melhem
Publisher :
ISBN 13 :
Total Pages : 92 pages
Book Rating : 4.3/5 (555 download)

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Download or read book Concrete Dead Load Deflections of Continuous Steel Girder Composite Bridges written by Hani Melhem and published by . This book was released on 1996 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: The changes in the properties of a multi-span continuous steel girder composite bridge during construction can cause final dead load deflections that are quite different from the calculated theoretical values. The casting rate and the sequence of span casting affect the development of concrete stiffness which can significantly affect the final dead load deflections. The study involved two activities: collecting data from the testing of concrete cylinders and laboratory-size beams representative of composite bridge girders and developing a computer program that calculates dead load deflections during construction based on the data from the laboratory testing. The 300 concrete cylinders were tested at ages varying from 2 to 36 hours after pouring to establish stress-strain relations in axial compression. The four composite beams (20 ft (6.1 m) long) with 16 strain gages and 4 deflection gages were tested by applying small incremental loads starting soon after the concrete was poured. Based on these measurements, the change in stiffness of the composite beam was computed and the concrete properties evaluated. The test results helped obtain a relationship that describes the variation of the concrete Young's Modulus with time varying from 2 to 36 hours. Best results were obtained between 4 and 19 hours. The relationship established seems logical and appeared to be consistent in all tests. It was implemented in the computer program and is most valid for ages up to 10 hours. The additional concrete stiffness gained after 10 hours is based on the slope of the curve at 10 hours and a limitation factor that determines the characteristic length of the transition polynomial and which specifies how soon the curve should be asymptotic to the standard value of the 28-days modulus of elasticity. The computer program was verified, however, additional research is needed to test the program more rigorously, to study the effect of concrete confinement and the use of plasticizers, and to compare the results of additional test data with actual field measurements. The effect of the weight of construction equipment should also be studied. Excessive bridge deflection could be avoided with a better understanding of the factors and parameters that affect the deflection.